Phylogenetic Placement of Whittingtonocotyle Neto, Rodrigues & Domingues, 2015 (Monopisthocotyla: Dactylogyridae) Inferred from the First Molecular Data of Both Described Species

Acta Parasitologica (2026) 71:59 https://doi.org/10.1007/s11686-026-01239-8 RESEARCH Phylogenetic Placement of Whittingtonocotyle Neto, Rodrigues & Domingues, 2015 (Monopisthocotyla: Dactylogyridae) Inferred from the First Molecular Data of Both Described Species Melissa Miyuki Osaki-Pereira1 · André Luiz Quagliatto Santos2 · Reinaldo José da Silva1 Received: 18 November 2025 / Accepted: 4 February 2026 / Published online: 9 March 2026 © The Author(s) 2026 Abstract Purpose This study provides the first molecular assessment of the two species of the genus Whittingtonocotyle, parasites of the erythrinid fish Hoplerythrinus unitaeniatus. The main objective was to evaluate the phylogenetic cohesion of Whittingtonocotyle and to explore its preliminary phylogenetic affinities within Dactylogyridae based on available molecular and morphological evidence. Methods Morphological examinations were performed in parallel with analyses of partial LSU rDNA and COI mtDNA sequences. Phylogenetic reconstructions were conducted independently for each marker to assess the monophyly of Whittingtonocotyle and to evaluate its relationships with other dactylogyrid taxa included in the available comparative dataset. Results Both molecular datasets consistently recovered Whittingtonocotyle as a strongly supported monophyletic lineage. In the phylogenetic reconstructions, Whittingtonocotyle was recovered in proximity to Urocleidoides species parasitizing erythrinid fishes, although deeper backbone relationships showed limited statistical support. Conclusion Morphological data support the recognition of Whittingtonocotyle as a distinct genus, whereas molecular analyses indicate a close phylogenetic proximity to erythrinid-associated Urocleidoides. This partial incongruence, together with the limited resolution of deeper relationships, highlights the need for expanded taxon sampling and multilocus datasets to fully resolve the evolutionary placement of Whittingtonocotyle within Dactylogyridae. Keywords Integrative taxonomy. phylogenetic relationships. erythrinid hosts. neotropical region. Introduction The family Erythrinidae comprises 21 freshwater fish species distributed across three genera and is endemic to South America [1, 2, 3]. Among them, Hoplerythrinus unitaeniatus (Spix & Agassiz, 1829) is widely distributed throughout the Amazon basin and in adjacent drainage systems, plays Melissa Miyuki Osaki-Pereira 1 Institute of Biosciences, Department of Biodiversity and Biostatics, Parasitology Section, São Paulo State University (UNESP), Botucatu, São Paulo State, Brazil 2 Wildlife Teaching and Research Laboratory, Faculty of Veterinary Medicine, Federal University of Uberlândia (UFU), Uberlândia, Minas Gerais State, Brazil an important ecological and economic role, particularly in small-scale fisheries [1]. Monopisthocotyls reported from erythrinid fishes currently belong to the genera Anacanthorus Mizelle & Price, 1965, Cosmetocleithrum Kritsky, Thatcher & Boeger, 1986, Gyrodactylus von Nordmann, 1832, Urocleidoides Mizelle & Price, 1964, Vancleaveus Kritsky, Thatcher & Boeger, 1986, and Whittingtonocotyle Neto, Rodrigues & Domingues, 2015[4, 5, 6, 7, 8]. However, molecular data for monopisthocotyls infecting erythrinids remain limited and unevenly distributed among taxa. To date, only nine dactylogyrid species parasitizing erythrinid fishes have been genetically characterized [9, 10], restricting broader phylogenetic inferences for this host-associated assemblage. Neto, Rodrigues and Domingues [4] proposed the genus Whittingtonocotyle based on two new monopisthocotyls species collected from H. unitaeniatus in northeastern Pará State, Brazil, with Whittingtonocotyle caetei Neto, 13 59 Page 2 of 10 Rodrigues & Domingues, 2015 as the type species. This genus was described exclusively based on morphological characters. It is characterized by a body divided into cephalic region, trunk, and haptor; a thin, smooth tegument; poorly developed or absent ventral cephalic lobes; two pairs of eyes with elongate granules; and a muscular, glandular pharynx with a short oesophagus. The intestinal caeca are paired, confluent posteriorly, and lack diverticula. The copulatory complex comprises a sclerotized, clockwise spiral male copulatory organ and a non-articulated accessory piece. The vagina is single, dextro-dorsal and marginal, with a heavily sclerotized sigmoid to coiled canal. The haptor bears 14 hooks, paired ventral and dorsal anchors without well-defined roots, and ventral and dorsal bars, the dorsal with an anteromedial process. Species of Whittingtonocotyle parasitize the gills of erythrinid fishes. Although this genus has been clearly delimited based on morphological evidence, its evolutionary relationships within Dactylogyridae remain poorly understood. A comprehensive phylogenetic framework for Dactylogyridae was proposed by Kmentová et al. [11]., however, Whittingtonocotyle could not be included in their analyses due to the absence of available DNA sequence data, and its molecular phylogenetic position therefore remained unresolved. In this study, we provide the first molecular data for Whittingtonocotyle by sequencing partial LSU rDNA and COI mtDNA from its two described species. The LSU rDNA marker has been widely used to infer phylogenetic relationships at higher taxonomic levels within Dactylogyridae, whereas COI mtDNA has been primarily applied to species delimitation and the assessment of genetic divergence among closely related taxa. Despite recent advances in the molecular phylogeny of Dactylogyridae, relationships among several lineages remain poorly resolved, particularly for genera parasitizing Neotropical freshwater fishes [12, 13, 14]. Within this context, the present study aims to provide an initial molecular placement of Whittingtonocotyle within the available phylogenetic framework of Dactylogyridae, evaluate its relative position among erythrinid-associated dactylogyrids, and integrate molecular and morphological evidence to improve our understanding of host associations and lineage diversity among South American freshwater monopisthocotyls. Materials and Methods Host and Parasite Sampling In March 2025, five individuals of H. unitaeniatus were obtained from the Pindaíba River, located in the 13 Acta Parasitologica (2026) 71:59 municipality of Cocalinho, Mato Grosso state, Brazil (14°31’40.1"S 51°41’35.0"W), through fishing using a cast net. Host specimens were identified to species level based on morphological characters. The sampling was carried out under authorization from the Brazilian Institute of Environment and Renewable Natural Resources (IBAMA; SISBIO license #60640-1). Fish were euthanized by severing the spinal cord and examined for parasites under a stereomicroscope. All experimental procedures were performed in accordance with the ethical standards established by the Ethics Committee on Animal Use (CEUA) of the University Center of Vale do Ara (...truncated)